Coaxial cable splice and methods of making it



COAXIAL CABLE SPLICES AND METHODS OF MAKING THEM Filed Feb. 8, 1949 y1953 c. E. LEWIS ET AL 2 Sheets-Sheet 2 lNl/ENTORS C. E. LE W/S W m E Fm 0 L V HE A TTORNE V Patented May 26, 1953 COAXIAL CABLE SPLICE ANDMETHODS OF MAKING IT Clay E. Lewis and Harold R. Longfellow, Baltimore,MILL, assignors to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Application February 8, 1949, Serial No.75,228

8 Claims.

This invention relates to cable splices and methods of making them, andmore particularly to splices for coaxial cable units and method ofmaking such splices.

Coaxial cables are used rather extensively in the transmission ofintelligence electrically and as high frequency transmission lines. Onetype of coaxial cable comprises a plurality of coaxial units, which aretwisted together and enclosed in a suitable insulating jacket, ormetallic sheath, or both. The individual coaxial units employed inmaking such coaxial cables consist ofa central conductor coaxiallypositioned within a tubular outer conductor having a longitudinal seam.Insulating discs spaced uniformly along the central conductor serve toseparate and align the inner and outer coaxial conductors. A pluralityof steel tapes are wound spirally around the tubular conductor, whichtapes act as a shield for the unit and also prevent the tubularconductors from being crushed during the twisting operation employed inmanufacturing coaxial cables.

Coaxia1 units are manufactured in lengths which will form coaxial cableshaving lengths required for installation in the field. It is oftennecessary to cut a manufactured length of coaxial unit to remove amechanical or electrical defect therein, in which case it is necessaryto splice the corresponding conductors of the two pieces of coaxialunits together to obtain a coaxial unit which may be incorporated in acoaxial cable.

Due to the fact that the individual coaxial units have steel tapes woundaround the tubular conductor and the fact that a plurality of the 1.

units are incorporated in a coaxial cable, the splice connecting thecoaxia1 units together must be made inside the tubular conductor so asnot to increase the diameter of the units at the splice. The splice alsomust not reduce materially the tensile strength of the coaxial unit.

In addition to these mechanical requirements, it is equally importantthat the physical structure of the splice must be such that it does notdisturb the critical electrical characteristics of the coaxial unit.Therefore, the splice must be of such construction that it does notmaterially increase the capacitance of the coaxial unit at the point ofthe splice. Furthermore, the splice must not have a lower dielectricstrength between Lil Another object of the invention is to provide newand improved splices for coaxial units and methods of making suchsplices.

A further object of the invention is to provide splices for coaxialunits which do not produce any enlargement of the diameter of the outerconductors joined together by the splice, provide adequate strength forthe spliced units, and provide good electrical continuity between thespliced conductors without materially increasing the capacitance of thecoaxial unit or reducing the dielectric strength of the unit at thesplice, and methods of making such splices.

One structure illustrating some of the features of the inventioncomprises a splice for coaxial units in which a butt-braze is formedbetween the center conductors of the coaxial unit to be spliced and ametallic band is brazed to the end portions of the tubular conductors insuch a position that the band is brazed to a substantial area of the endportion of each tubular conductor.

One method of splicing such cables, which illustrates features of theinvention, comprises butt-brazing the ends of the center conductors andbrazing a metallic band to the end portions of the tubular conductors ofthe coaxial units in such a position that the band is brazed to asubstantial area of the end portions of the tubular conductors.

A clear understanding of the invention will be had from the followingdetailed description of a specific structure embodying the invention anda method of making the same, which embodies the invention, and from theappended drawings, in which:

Fig. l is a perspective view of a portion of a typical coaxial unitwhich may be spliced by the use of apparatus and methods embodying theinvention;

Fig. 2 is a front elevation of an apparatus in which the ends of twocoaxial units may be secured during a splicing operation;

Fig. 3 is an enlarged, fragmentary, top plan view showing the endportions of two coaxial units during an early stage in the production ofa splice between the coaxial units;

Fig. 4 is an enlarged, perspective view of an insert positioned in oneof the coaxial units as shown in Fig. 3;

Fig. 5 is an enlarged, perspective view of a laminated ring used tosplice the end portions of the tubular conductors of the coaxial unitsshown in Fig. 3

ductor as shown in Fig. 3.

Fig. 6 is an enlarged, vertical section taken along line 6 of Fig. 3;

Fig. 7 is an enlarged, fragmentary view of a completed splice betweentwo coaxial units with a portion thereof broken away to show theinternal structure of the splice;

Fig. 8 is an enlarged, vertical section taken along line 8-8 of Fig. '7;

Fig. 9 is a fragmentary view of the coaxial unit splice with portionsthereof broken away to show the connection between the steel tapes ofthe spliced coaxial units, and

Fig. 10 is an enlarged, sectional view taken along line |ilil of Fig. 9.

Referring now to the drawings and particularly to Fig. 1, there is showna portion of one type of coaxial unit indicated generally by the numerall6, which is used in the manufacture of coaxial cables. The coaxial unitl0 consists of a center conductor |2 coaxially positioned. within atubular outer conductor is by means of insulating discs |(3|5 spaceduniformly along the center conductor. In the manufacture of theindividual coaxial units, the tubular conductor i5 is formedlongitudinally around the discs iii-l5 from a thin copper tape. wherebythe opposite sides of the tape form a longitudinal seam i'i alongthe'tubular conductor. After the tubular conductor i5 is formed aroundthe insulating discs |6--|6, an inner layer of steel tape Zll and anouter layer of steel tape 2! are wound spirally around the tubularconductor S5 for the purpose of shielding and protecting it.

A plurality of coaxial units like the coaxial unit Ill, are twistedtogether and enclosed in an insulating jacket anda lead sheath to formcoaxial cables of specified lengths. To manufacturecoaxial cables ofspecified length, it is often necessary to splice two lengths of coaxialunits like the coaxial unit M, to obtain a length of coaxial unit whichmay be incorporated in a coaxial cable.

Two coaxial units or portions ofa coaxial unit, like the coaxial unit In(Fig. 1) may be spliced together inthe following manner:

The end portions of two coaxial units Ill-l9 (Fig. 2) to be spliced, aresecured in supports 2525 provided on the top of a work bench 28 in sucha-position that the adjacent ends of the coaxial units do not contacteach other. tachable type of clamp, indicated generally at 2'1, isattached to each coaxial unit II! at a point adjacent to its respectivesupportZE and the steel tapes 2B and 2| are unwound from the end of eachtubular conductor of the coaxial units back r to the clamp 27 andallowed to hang from the coaxial unit in the form of curls. The clamps2'|2i are attached to the coaxial units to prevent further unwinding ofthe steel tapes 2!] and 2| from their respective tubular conductors.

After the steel tapes and 2| have been removed to expose the ends of thetubular conductors, each coaxial unit is adjusted in its respectivesupport so that their respective longitudinal seams are aligned alongthe top side of the tubular conductors with respect to the work bench25.

A small length is removed from the end of each tubular conductor l5 anda relatively smaller length is removed from each center conductor l2 sothat the end of each center conductor l2 extends slightly beyond itsrespective tubular con- Care must be taken to insure that the end ofeach tubular conductor A de- |5 and the end of each center conductor I2is cut oil? square.

After the ends of the tubular conductors have been prepared in thismanner, a split znetal block 33 is clamped to each tubular conductor l5a short distance from the end thereof for the purpose of absorbing theheat applied to the tubular conductors during the brazing operationhereinafter described. The longitudinal seam oi each tubular conductoris opened from the end thereof to its respective block 30 so that theend of each tubular conductor is substantially U- shaped, as shown inFigs. 3 and 6, and the end of its center conductor l2 and the insulatingdiscs |E-|S areexposed. The exposed insulat ing discs then are slidtoward the closed portion of the tubular conductors to clear the endportions of the center conductors, and a ceramic bushing .3l (Figs. 3and 6) is positioned over the center conductor of one of the coaxialunits and slid therealong until it engages a disc H5 at the innerend ofthe open portion of the tubular conductor.

The bushing 3| (Figs. 3, i and 7) is provided with a central hub 32having a bore 33 therethrough for receiving the center conductor i: ofthe coaxial unit and a peripheral groove 34 equidistant from the endsthereof. The central portion of the bushing is of such diameter that itfits snugly into the tubular conductors, whereas the end portionsthereof are tapered to provide an annular-clearance between the tubularconductor and the ends of the bushing. The bushing 3| is made of aceramic material having a high dielectric strength, and capable ofwithstanding the heat encountered in brazing metals with silver solderor the like.

Before the bushing i'llis positioned in the end of one of the coaxialunits as described, a split laminated ring .3"! (Fig. 5) is positionedin the peripheral groove of the bushing as shown in Fig. 4. Thelaminated ring 31 consists of a split copper band 38 surrounded by asplit silver solder band 40, the two bands being spotwelded together atH so as to align the open ends of the bands to form a slit 42 in thelaminated rin .37.

The peripheral groove 34 is of such depth that the ring 31 may bepositioned therein without any portion thereof extending beyond theperiphery of the bushing 3| After the ceramic bushing 3|, having thelaminated ring 31 assembled thereon, is positioned in the open end ofone of thetubular conductors as shown in Fig. 3, a disc of silver solderis held against the center conductor i2 of the other coaxial unit. Thecoaxial unit having the bushing 3'1 positioned therein then is unclampedfrom its support 25, moved until its center conductor engages the silversolder disc and then is clamped to hold the disc between the centerconductors. Suitable electrodes are attached to the ends ofthe centerconductors and are connected electrically to a conventional micro-weldercapable of passing sufiicient current through the silver solde disc tomelt it and form a brazed joint 45 (Fig. 3) between the centerconductors. Any excess silver solder at the joint 45 is swaged down sothat the diameter of the joint is equal to the diameter of the centerconductors.

After the brazed joint 35 (Fig. 3) has been completed as described, theceramic bushing 3| is moved along the center conductor l2 on which it ispositioned until the hub portion 32 thereof is divided equally bythe-brazed joint as shown in Fig. '7. When the bushing 3| is positionedin this manner, the laminated ring 31 positioned in the groove 34,extends an equal distance along each of the tubular conductors l5l5. Thelaminated ring 3'! is so positioned on the bushing 25 that the slit 42straddles the line of the longitudinal seams I1-Il (Fig. 8) of thetubular conductors. The insulating discs I 6l6, which were slid awayfrom the ends of the center conductors, are moved into equidistantpositions on the center conductors with one of the discs of each coaxialunit positioned against an end of the bushing 3|, as shown in Fig. 7.After the laminated ring 31 has been positioned in this manner, theopened ends of the tubular conductors are closed carefully so that theends of the conductors are in substantially the same form as they wereprior to being opened.

Brazing electrodes of standard design (not shown) are clamped around theperiphery of the tubular conductors so that equal portions of theadjacent ends of the tubular conductors are engaged by the electrodes.The electrodes are connected electrically to a conventional weldingtransformer (not shown), and the electrodes and the end portions of thetubular conductors l5 -l 5 clamped therein are heated sufiiciently tomelt the silver solder band 40 and braze the copper band 38 to theinside surfaces of the tubular c'on ductors as shown in Fig. '7.

The ceramic bushing 3! serves to prevent the electrodes from crushingthe tubular conductors and to hold the laminated ring 31 in place whilethe heat is being applied to cause the silver solder band to melt andbraze the tubular conductors to the copper band. Excessive heat maydangerously affect the insulating quantity of the discs I6I5 and thestructural quantity of the tubular conductors. To prevent damage to theunit by heat, the metallic blocks 3030 are attached to the tubularconductors to absorb the heat applied to each tubular conductor andthereby prevent excessive heat from flowing along the tubular conductorsbeyond the point at which the braze is made.

When the end portions of the tubular conductors have been brazed to thecopper band, a complete splice, indicated generally at 46 (Fig. 7), hasbeen made between the center conductors l2l2 and the tubular conductorsl5l5 of the coaxial units Ill-l0. After the splice 46 (Fig. 7) has beencompleted, the inner steel tape 20 of each coaxial unit is rewoundaround its respective tubular conductor and the excess portions of eachtape are cut off square so that the ends of the corresponding tape abutas indicated by the numeral 50 in Fig. 9. The corresponding ends of eachtape 20 then are perforated to provide slots 5l5|, and a metal tape 52is laced through the slots '5l-5| in the manner shown in Fig. 10 to holdthe tapes together. Several layers of pressure-sensitive tape 53, suchas a cellulose strip covered on one side with a pressure sensitiveadhesive, are wound around the laced joint of the tapes to hold it inplace. One particular type of tape that has been found satisfactory forthis purpose is a pressure sensitive tape manufactured by the MinnesotaMining & Mfg. Co., St. Paul, Minnesota, under the trade name of ScotchElectrical Tape. ends of inner steel tape are laced together in thismanner, the outer steel tape 2| of each coaxial unit then is rewound soas to overlap the tape 20. The excess portions of the ends of each Afterthe tape 2| are cut off square, and the ends of the tapes 2l2| areslotted and laced together in the same manner as that described for thetape 20. The laced joints between the tapes 2!) and2l are staggeredalong the coaxial unit so that they do not overlap and produce anyenlargement of the coaxial units at the splice 46. Since material is cutfrom the end of each conductor i5 and from the end of each centerconductor 12 after the steel tapes 20 and 2| have been removed to exposethe ends of the tubular conductors, both tapes 20 and 2| contain excesslengths of tape when rewound about the tubular conductors l5-l5. Hence,the staggering of the joints between the tapes 20 and 2| may be easilyaccomplished. The staggering of the joints between the tapes 20 and 2|may also be accomplished by cutting the tapes, prior to their removal,at staggered points along the length of the coaxial unit. Hence, whenthe tapes 20 and 2| are rewound, their joints necessarily will bestaggered.

The bushing 31, forming part of the splice 46, is designed to maintainconcentricity between the conductors of the coaxial unit at the spliceand to support the end portions of the tubular conductors which areannealed by the heat applied to braze the conductors to the copper band.Since the end portions of the bushing are tapered,

the splice may be flexed sufliciently to allow the coaxial unitcontaining the splice to be wrapped around a takeup reel, in which case,the body of the bushing prevents the end portions of the tubularconductors from buckling when the splice 46 is flexed.

Silver solder is used to form the brazed joint 45 and to braze thetubular conductors to the copper band in order to obtain good electricalconductivity at the brazed joints and at the same time produce a splicewhich does not reduce appreciably the tensile strength of the coaxialunit. The brazed joint between the tubular conductors and the copperband is not extended across their respective longitudinal seams becausethe opposite sides of the seams must be free to slide a certain amountwith respect to each other when the spliced coaxial unit is twistedtogether with other coaxial units to form the core of a coaxial cable.Since the splice 46 introduces only a very small amount of materialhaving a low dielectric constant between the center conductor andtubular outer conductor of a coaxial unit, the splice does not increasematerially the capacitance of the coaxial unit at the splice and doesnot reduce the dielectric strength of the coaxial units at the splice.

The ceramic bushing is of such material and so designed that it preventsthe reduction of the dielectric strength of the coaxial unit at thesplice.

What is claimed is:

1. A splice for coaxial units each having an outer tubular conductor andan inner wire conductor disposed in concentric relation with respect toeach other, which comprises a brazed joint between the wire conductorsof two such coaxial units to be spliced, a non-conductive, annularmember positioned over the brazed joint of the wire conductors so thatit extends an equal distance into each tubular conductor, and a metallicband positioned around the annular memher and brazed to the innersurface of the end portions of the tubular conductors, said annularmember being of such dimensions to hold the metallic band in placeagainst the inside surfaces of the tubular conductors while the band isbrazed to the tubular conductors and for maintaining concentricitybetween the wire conductors and the tubular conductors so that the 7splice does not reduce the dielectric strength of or increase materiallythe capacitance of the cables at the splice.

2. A splice for coaxial units each having a tubular conductor and aninner wire conductor disposed in concentric relation with each other,which comprises a butt-braze between the ends of the wire conductors oftwo such coaxial units to be spliced, a non-conductive bushing havingtapered ends positioned over the brazed joint between the wireconductors so that it extends an equal distance into each tubularconductor, said bushing having a diameter substantially equal to theinside diameter of the tubular conductors of the said coaxial units anda peripheral groove around the central portion thereof, and a cop perband positioned in the peripheral groove of the bushing and brazed tothe tubular conductors in such a position that the band is brazed to asubstantial area of the inner surface of each end portion of the tubularconductors, said peripheral groove of the bushing being of such depththat it holds the copper band against the tubular conductors andprevents them from being deformed when the band is brazed to theconductors.

A splice for coaxial units having an inner wire conductor concentricallydisposed within an outer tubular conductor having a longitudinal seam,which comprises a brazed joint between the wire conductors of two suchcoaxial units to be spliced, a non-conductive annular member positionedover the brazed joint of the wire conductors so that it extends intoeach tubular conductor, and a split metallic band positioned around theannular member and brazed to the inner surfaces of the end portions ofthe tubular conductors in such a position that the brazed joint does notextend across the longitudinal seams of the tubular conductors, saidannular member serving to hold the split metallic band in place againstthe inside surface of the tubular conductors while the band is brazed tothe tubular conductors and for maintaining concentricity between thewire conductor and the tubular conductor at the splice.

4. A splice for coaxial units each comprising a center conductorconcentrically disposed within a tubular conductor having a longitudinalseam, which comprises a butt-brazed joint between the wire conductors oftwo such coaxial units to be spliced, a ceramic tubular member havingtapered ends positioned in the end portions of the tubular conductors soas to cover the brazed joint between the center conductors, said tubularmember having a diameter substantially equal to the inside diameter ofthe tubular conductors of the coaxial units and a peipheral groovepositioned centrally with respect to the ends of the tubular member, anda split copper band positioned in the peripheral groove and brazed tothe inside surface of the end portions of the tubular conductors in sucha position that the copper band does not extend across the longitudinalseam of the tubular conductors, said annular groove in the tubularmember serving to hold the split copper band in position when the copperband is brazed to the tubular conductors, whereby the wire conductorsand tubular conductors of the coaxial units are spliced together withoutenlarging the outside diameter of the coaxial units at the splice.

5. An insert for forming internal splices between metallic tubularmembers, which comprises an annular, ceramic member having a perlpheralgroove formed equidistant from the end thereof and having its endstapered inwardly, and a split, laminated ring positioned in theperipheral groove and consisting of a split metallic band and a splitsilver solder band spot welded to each other, whereby when the insert isp0- sitioned within the end portions of two tubular members to bespliced the metallic band may be brazed to the inner surface of eachtubular conductor by melting the silver solder band.

6. A splice for coaxial units having an outer tubular conductor and acenter wire conductor disposed in concentric relation with respect toeach other, which comprises a brazed joint between the ends of the wireconductors of two such coaxial units to be spliced, a nonconductivebushing positioned so that the ends thereof extend into the tubularconductors, said bushing having an outer diameter substantially equal tothe inner diameter of the tubular conductors of said coaxial units and aperipheral groove around the central portion thereof, and a metallicband positioned in the peripheral groove of the bushing and brazed tothe tubular conductors in such a position that the band is brazed to asubstantial area of the inner surfaces of the adjacent end portions ofthe tubular conductors, said peripheral groove of the bushing being ofsuch depth that it holds the metallic band against the tubularconductors and prevents the tubular conductors from being deformedduring the brazing operation.

'7. The method of splicing coaxial units each having a center conductorcoaxially surrounded by tubular conductor having longitudinal seam andplurality of steel tapes spirally wound around the tubular conductor,which comprises sli ng the steel tapes backv from the end of each or alunit a predetermined distance, squaring the ends of tubular conductorsto be spliced, openin the end of the tubular conductor of each coaxialunit to permit access to the center conductors, positioning a ceramicbushing on the end of the center conductor of one of the coaxial units.said bushing having a peripheral groove spaced equidistant the ends ofthe bushing, and positioning a split laminated ring in the annulargroove of the bushing, said laminated ring comprising a split copperband surrounded. by a split silver solder band and spot welded theretoso as to align the open end of the bands with each other, brazing theends of the center conductors, sliding the bushing over the brazed jointof the center conductors so that the open end 01' the laminated ringstraddles the longitudinal seam of the tubular conductors, closing theends of the tubular conductors around the bushing, and applyingsuflicient heat around the end portions of the tubular conductors incontact with the laminated ring to melt the silver solder band and brazethe copper band to the inside surface of the tubular conductors so thatthe brazed. joint does not extend across the longitudinal seam of thetubular conductors, said ceramic bushing being designed to prevent areduction in the dielectric strength of the coaxial units at the splice.

S. lhe method of splicing cables having a center conductor positionedcoaxially Within an outer tubular conductor having a longitudinal seam,which comprises forming a butt-braze between the ends of the centerconductors of two such cables to be spliced, positioning anon-conductive annular member over the brazed joint between the centerconductors so that it extends a substantial distance into each of thetubular conductors to be spliced, said annular member having aperipheral groove therein, positioning a split metallic band in theperipheral groove of the annular member, and brazing the metallic bandto the inner surface of the end portion of each tubular conductor insuch a position that the hand does not extend across the longitudinalseam of the tubular conductors, said annular member being designed tosupport the metallic band when it is brazed to the end portions of thetubular conductors and to maintain concentricity between the centerconductors and the tubular conductors at the splice.

CLAY E. LEWIS.

HAROLD R. LONGFELLOW.

References Cited in the file of this patent UNITED STATES PATENTS Number5 525,670 1,876,585 2,050,728 2,123,061 2,156,772 10 2,372,645 2,439,8412,468,783

Number 15 21,410

